The present invention relates to an apparatus for controlling stiffness of a vehicle body, which is applied to a vehicle equipped with shock absorbing structure. The apparatus is able to control stiffness of a frame and the like of the vehicle body so as to provide appropriate reaction force according to collisions and colliding objects.
An apparatus for controlling stiffness of a vehicle body has been known, which has piezoelectric actuators for controlling stiffness of right and left side frames. An actuator, which is mounted to each side frame, selectively provides resistive force against impact force, which acts on the front of a vehicle in a backward direction, or assisting force for it according to collisions. Japanese Published Patent Application H11-291951 discloses related arts. The document discloses an apparatus which controls stiffness of side frames in the following manner. In case of a full wrap collision, in which the whole front of a vehicle is involved, the apparatus decreases the stiffness of side frames. On the other had, in case of an offset collision, in which impact force locally acts on one of the side frames, the apparatus increases their stiffness. In this way, the apparatus provides optimal shock absorption according to collisions.
The apparatus described above is able to vary stiffness of a vehicle according to sizes of colliding objects so as to control resistive force acting on a colliding object in addition to selection of stiffness according to collisions such as full wrap and offset collisions.
However, the apparatus described above requires a large amount of power to drive the piezoelectric actuator, which generates the resistive force against the impact force. This results in a drawback that the size of the piezoelectric actuator and the size of a battery for supplying power to it inevitably tend to increase.